Ion detectors and methods of using them

ABSTRACT

Certain embodiments described herein are directed to ion detectors and systems. In some examples, the ion detector can include a plurality of dynodes, in which one or more of the dynodes are coupled to an electrometer. In other configurations, each dynode can be coupled to a respective electrometer. Methods using the ion detectors are also described.

PRIORITY APPLICATIONS

This application claims priority to each of U.S. Patent Application No.61/728,188 filed on Nov. 19, 2012, to U.S. Patent Application No.61/732,865 filed on Dec. 3, 2012 and to U.S. Patent Application No.61/781,963 filed on Mar. 14, 2013, the entire disclosure of each ofwhich is hereby incorporated herein by reference for all purposes.

TECHNOLOGICAL FIELD

Certain features, aspects and embodiments are directed to ion detectorsand methods of using them. In some instances, the ion detector can beconfigured to amplify a signal using a plurality of dynodes.

BACKGROUND

In many instances it is often desirable to detect ions. Ions signals areoften amplified using an electron multiplier to permit their detection.

SUMMARY

Certain aspects described herein are directed to detectors that canreceive ions, measure signals from analog dynode stages and can shunt orshut down dynodes downstream of a saturated dynode to protect thedynodes of the detector. In some configurations, the detector isconfigured to function without any pulse counting, e.g., comprises onlyanalog stages and no pulse counting stage or pulse counting electrode,and may measure a plurality of analog signals, scale each signal andaverage the signals. By measuring the input or output current tomultiple dynodes, and shutting down high current dynodes, the dynamicrange of the detector can be extended and linearity can be improved. Thevarious measured dynodes may be electrically isolated from each other sothat separate signals can be measured or detected. In some instances,the circuitry for each dynode may be electrically isolated orelectrically insulated from the circuitry of other dynodes to permitmeasurement of each dynode or a desired number of dynodes. For example,supply currents at each dynode (or selected dynodes) can be measured andused to determine an ion level, and the detector can terminate signalamplification at a measured, saturated dynode to protect dynodesdownstream of the saturated dynode.

In a first aspect, a mass spectrometer comprising a sample introductionsystem, an ion source fluidically coupled to the sample introductionsystem, a mass analyzer fluidically coupled to the ion source, and adetector fluidically coupled to the mass analyzer is provided. Incertain configurations, the detector comprises an electron multipliercomprising a plurality of dynodes each electrically coupled to arespective electrometer.

In certain embodiments, the mass spectrometer comprises a firstprocessor electrically coupled to each electrometer. In otherembodiments, the first processor is configured to measure the input oroutput current at each respective dynode. In some examples, the firstprocessor is configured to calculate a mean input current using receivedinput current signals and using the gain of the respective dynode. Inother examples, the first processor is configured to calculate a gainbetween consecutive dynodes by comparing a current, e.g., input oroutput current, of the first dynode to a current, e.g., input or outputcurrent, of a dynode immediately upstream of the first dynode. In someexamples, each electrometer is electrically coupled to a signalconverter to provide simultaneous signals, e.g., digital signals, to theprocessor from each of the plurality of dynodes. In further examples,the signal converter comprises an analog-to-digital converter or an ionpulse counter or other suitable signal converters. In some embodiments,the detector further comprises a respective power converter electricallycoupled to each electrometer and converter pair. In other examples, thefirst processor is configured to measure all dynode currentssimultaneously. In some embodiments, the detector (or first processor orboth) is configured to prevent a current overload at each dynode.

In certain configurations, the detector (or first processor or both) isconfigured to alter the voltage of a saturated dynode (relative to aprevious, upstream dynode), to reduce its electron gain to the previousdynode, and/or reduce the ion current for downstream dynodes. In someembodiments, the detector (or first processor or both) is configured toinvert the polarity of the voltage to the previous dynode or to asubsequent dynode or both. In other embodiments, the detector (or firstprocessor or both) is configured to prevent any substantial secondaryelectron emission to a downstream dynode adjacent to the dynode wherethe saturation current is detected. In some examples, voltage of theelectron multiplier is not adjusted between measuring species havingdifferent mass-to-charge ratios. In certain embodiments, the gain of theelectron multiplier is constant. In other embodiments, gain of theelectron multiplier is not user adjustable. In some examples, theelectron multiplier is configured to provide independent voltage controlat each dynode of the plurality of dynodes. In further examples, dynodeto dynode voltage can be regulated to keep the voltage substantiallyconstant (or constant) while allowing variable the input or outputcurrent of each dynode. In certain examples, dynamic range of ioncurrent measurements is greater than 10⁸, 10⁹ or 10¹⁰ when measuring theion current at a rate of 100 kHz. In other embodiments, the signal fromevery electrometer is used by the first processor to calculate a meanelectron multiplier input current. In some embodiments, the firstprocessor is configured to calculate the mean electron multiplier inputcurrent by calculating the input currents of the dynode signals whichare above a minimum noise threshold and below a maximum saturationthreshold.

In an additional aspect, a mass spectrometer comprising a sampleintroduction system, an ion source fluidically coupled to the sampleintroduction system, a mass analyzer fluidically coupled to the ionsource, and a detector fluidically coupled to the mass analyzer, inwhich the detector comprises a plurality of continuous electronmultiplier sections, e.g., where each comprise a plurality of dynodes,in which at least one section of the plurality of dynodes iselectrically coupled to an electrometer is described.

In certain embodiments, the mass spectrometer comprises at least oneadditional electrometer electrically coupled to one of the plurality ofdynodes. In some embodiments, a first processor is electrically coupledto each electrometer and is configured to measure a current, e.g., inputor output current, into/from each respective dynode. In certainexamples, at least one dynode without a respective electrometer ispositioned between dynodes that are electrically coupled to anelectrometer. In some examples, one or more of the sections may comprisea plurality of electrometers, in which every other dynode iselectrically coupled to an electrometer. In certain examples, one ormore sections comprise a plurality of electrometers, in which everythird dynode electrically coupled to an electrometer. In someembodiments, one or more sections comprise a plurality of electrometers,in which every fourth dynode electrically coupled to an electrometer. Inother embodiments, the one or more sections comprise a plurality ofelectrometers, in which every fifth dynode electrically coupled to anelectrometer. In some embodiments, each electrometer is electricallycoupled to a signal converter. In other examples, each electrometer iselectrically coupled to an analog-to-digital converter, an ion pulsecounter or other suitable converters to provide, for example,simultaneous digital signals to the processor from each of the dynodeselectrically coupled to an electrometer. In certain examples, theprocessor is configured to provide a mean digital signal representativeof the concentration of the sample using the simultaneous digitalsignals. In some examples, the mass spectrometer comprises a processorelectrically coupled to the plurality of dynodes and configured toprevent a current overload at one or more dynodes or at each dynode. Incertain examples, the detector (or processor or both) is configured toalter the voltage of a saturated dynode (relative to a previous dynode)to reduce its electron gain to the previous dynode and reduce the ioncurrent for other downstream dynodes. In some embodiments, gain (orvoltage) of the electron multiplier is not adjusted between measuringspecies having different mass-to-charge ratios. In other embodiments,the gain of the electron multiplier is constant or not user adjustable.In some examples, the electron multiplier is configured to provideindependent voltage control at each dynode of the plurality of dynodes.In certain examples, dynode to dynode voltage is regulated to keep thevoltage substantially constant (or constant). In other examples, dynamicrange of ion current measurement is greater than 10⁸, 10⁹, or 10¹⁰ whenmeasuring the ion current at a rate of 100 kHz. In some examples, thesignal from every electrometer is used by the processor to calculate amean electron multiplier input current. In additional examples, thefirst processor is configured to calculate the mean electron multiplierinput current by calculating the input currents of dynode signals whichare above a minimum noise threshold and below a maximum threshold, e.g.,by discarding input currents below a noise current and above asaturation current. In some embodiments, the first processor isconfigured to scale each non-discarded calculated input current usingthe respective electron multiplier gain and average the scaled inputcurrents to provide the mean electron multiplier input current.

In another aspect, a detector comprising an electron multipliercomprising a plurality of dynodes each configured to electrically coupleto a respective electrometer is described. In some embodiments, theplurality of dynodes and the electrometers are in the same housing. Inother embodiments, each electrometer is electrically coupled to arespective signal converter. In some examples, each of the respectivesignal converters is an analog-to-digital converter. In some examples,each of the respective signal converters is an ion pulse counter orother suitable signal converter. In further examples, each of theanalog-to-digital converters or ion pulse counters is configured totransmit its data in an electrically isolated manner to a firstprocessor. In some embodiments, the detector comprises a respectivepower converter electrically coupled to each electrometer andanalog-to-digital converter pair. In some configurations, for one ormore dynodes, e.g., each dynode, the electrometer and the converter canbe at substantially the same electrical potential, e.g., where theprocessor is at ground potential. In certain embodiments, the detectorcomprises a processor electrically coupled to each of the plurality ofdynodes and configured to prevent a current overload at each dynode. Inother examples, the processor is configured to alter the voltage at,upstream or downstream of a dynode where a saturation current isdetected. In some examples, the processor is configured to invert thepolarity of a voltage of the downstream dynode. In further examples, thefirst processor is configured to prevent any substantial secondaryelectron emission to a downstream dynode adjacent to the dynode where asaturation current is detected.

In an additional aspect, a detector comprising an electron multipliercomprising a plurality of dynodes each electrically coupled to arespective electrometer configured to provide an output signal isdescribed. In certain embodiments, the plurality of dynodes and theelectrometers are in the same housing. In other embodiments, eachelectrometer is electrically coupled to a respective signal converter.In some embodiments, each of the respective signal converters is ananalog-to-digital converter, an ion pulse counter or other suitablesignal converter. In further examples, each of the analog-to-digitalconverters is configured to electrically couple to a first processor,e.g., in an electrically isolated manner. In some examples, the detectorcomprises a respective power converter electrically coupled to eachelectrometer and signal converter pair. In further examples, thedetector comprises a first processor electrically coupled to each of theplurality of dynodes and configured to prevent a current overload ateach dynode. In some embodiments, the processor is configured to alterthe voltage of a saturated dynode (relative to a previous dynode) toreduce its electron gain to the previous dynode and reduce the ioncurrent for other downstream dynodes. In certain examples, the processoris configured to invert the polarity of the voltage to the previousdynode or to a downstream dynode or both. In some examples, theprocessor is configured to prevent any substantial secondary electronemission to a downstream dynode adjacent to a dynode where a saturationcurrent is detected.

In another aspect, a detector comprising a single-stage electronmultiplier comprising a plurality of dynodes, in which at least oneinternal dynode of the plurality of dynodes is configured toelectrically couple to an electrometer is provided In some examples, atleast two of the internal dynodes of the plurality of dynodes areconfigured to electrically couple to a respective electrometer. In otherexamples, every other dynode of the plurality of dynodes is configuredto electrically couple to a respective electrometer. In furtherexamples, every third dynode of the plurality of dynodes is configuredto electrically couple to a respective electrometer. In someembodiments, the electrometer is configured to electrically couple to asignal converter. In certain embodiments, the signal converter is ananalog-to-digital converter, an ion pulse counter or other suitablesignal converters. In certain examples, the detector comprises a powerconverter electrically coupled to the electrometer and to the signalconverter. In some embodiments, the detector comprises a first processorelectrically coupled to each of the plurality of dynodes (e.g., whereeach dynode is electrically isolated from other dynodes to provideseparate signals to the processor) and configured to prevent a currentoverload at each dynode. In some examples, the processor is configuredto measure all dynode currents simultaneously. In certain examples, theprocessor is configured to alter the voltage at a saturated dynode(relative to the previous dynode) to reduce its electron gain to theprevious dynode and reduce the ion current for downstream dynodes.

In an additional aspect, a detector comprising a single-stage electronmultiplier comprising a plurality of dynodes, in which at least oneinternal dynode of the plurality of dynodes is electrically coupled toan electrometer is provided. In certain embodiments, at least two of theinternal dynodes of the plurality of dynodes are electrically coupled toa respective electrometer. In other embodiments, every other dynode ofthe plurality of dynodes is electrically coupled to a respectiveelectrometer. In some examples, every third dynode of the plurality ofdynodes is electrically coupled to a respective electrometer. Inadditional examples, the electrometer is electrically coupled to asignal converter. In further examples, the signal converter is ananalog-to-digital converter, an ion pulse counter or other suitablesignal converters. In other embodiments, the detector comprises a powerconverter electrically coupled to the electrometer and to the signalconverter. In some embodiments, the detector comprises a processorelectrically coupled to each of the plurality of dynodes and configuredto prevent a current overload at each dynode. In other embodiments, theprocessor is configured to measure all dynode currents simultaneously.In some examples, the processor is configured to alter the voltage at asaturated dynode (relative to a previous dynode) to reduce its electrongain to the previous dynode and reduce the ion current for dynodesdownstream of the saturated dynode.

In another aspect, a method of detecting ions comprising simultaneouslydetecting a current signal (an input current signal or output currentsignal) at each dynode of a plurality of dynodes of an electronmultiplier configured to receive ions, and averaging the detectedcurrent signals at each dynode comprising a measured current signalabove a noise current signal and below a saturation current signal todetermine a mean electron multiplier current is provided. In certainexamples, the method comprises terminating signal amplification at adynode where a saturation current is detected/measured or at a dynodeupstream where the saturation current is measured. In other examples,the method comprises altering the voltage at a downstream dynodeadjacent to the dynode where the saturation current is measured toterminate the signal amplification. In certain configurations, themethod comprises altering the voltage at an upstream dynode adjacent tothe dynode where the saturation current is measured to terminate thesignal amplification. In some embodiments, the method comprisescalculating the mean current by calculating the currents at all dynodesand discarding calculated currents below the noise current signal andabove the saturation current signal. The method may also include scalingeach non-discarded calculated current by its respective electronmultiplier gain and averaging the scaled currents to provide the meanelectron multiplier current. In certain embodiments, the methodcomprises providing a floating voltage to each dynode of the pluralityof dynodes. In other embodiments, the method comprises controlling thevoltage at each dynode independently of voltage at the other dynodes ofthe plurality of dynodes. In some examples, the method comprisesmeasuring the ions without adjusting the voltage of the electronmultiplier. In further examples, the method comprises measuring aplurality of ions comprising different mass-to-charge ratios withoutadjusting the voltage of the electron multiplier. In other examples, themethod comprises calculating the amount of ions of a selectedmass-to-charge ratio using the calculated mean current. In certainembodiments, the method comprises calculating the amount of ions persecond of a selected mass-to-charge ratio using the calculated meancurrent.

In an additional aspect, a method of detecting ions comprisingsimultaneously detecting a current signal (input current signal oroutput current signal) of at least two internal dynodes of a pluralityof dynodes of an electron multiplier configured to receive ions, andaveraging the detected current signals at each of the at least twointernal dynodes comprising a measured current signal above a noisecurrent signal and below a saturation current signal to determine a meanelectron multiplier input current is disclosed. In certain embodiments,the method comprises terminating signal amplification at a dynode wherea saturation current is measured. In other embodiments, the methodcomprises simultaneously detecting a current signal (input currentsignal or output current signal) at every other internal dynode of theplurality of dynodes. In further embodiments, the method comprisessimultaneously detecting a current signal at every third internal dynodeof the plurality of dynodes. In additional examples, the methodcomprises terminating signal amplification at a dynode where asaturation current is measured. In some embodiments, the methodcomprises providing a floating voltage at each detected dynode of theplurality of dynodes. In other embodiments, the method comprisescontrolling the voltage at each dynode independently of voltage at theother dynodes of the plurality of dynodes. In some examples, the methodcomprises measuring the ions without adjusting the gain of the electronmultiplier. In additional embodiments, the method comprises calculatingthe mean input current by calculating the input currents at selecteddynodes and discarding calculated input currents below the noise currentinput signal and above the saturation current input signal, and scalingeach non-discarded calculated input current by its respective electronmultiplier gain and averaging the scaled input currents to provide themean electron multiplier input current. In other examples, the methodcomprises configuring the dynamic range of ion current measurement isgreater than 10¹⁰ when reading the ion current at a rate of 100 kHz.

In another aspect, a method of detecting ions comprising simultaneouslydetecting an input current signal (or output current signal) of at leasttwo internal dynodes of an electron multiplier configured to receiveions, and averaging the detected input current signals at each of the atleast two internal dynodes comprising a measured current input signalabove a noise current input signal and below a saturation current inputsignal to determine a mean input current is disclosed. In certainexamples, the method comprises terminating signal amplification at adynode where a saturation current is measured or terminating signalamplification at a dynode immediately upstream or downstream of where asaturation current is measured. In other examples, the method comprisessimultaneously detecting an input current signal (or output currentsignal) at every other internal dynode of the plurality of dynodes. Infurther examples, the method comprises simultaneously detecting an inputcurrent signal (or output current signal) at every third internal dynodeof the plurality of dynodes. In some embodiments, the method comprisesterminating signal amplification at a dynode where a saturation currentis measured. In certain embodiments, the method comprises providing afloating voltage at each detected dynode of the plurality of dynodes. Inother embodiments, the method comprises controlling the voltage at eachdynode independently of voltage at the other dynodes of the plurality ofdynodes. In further examples, the method comprises measuring ions havinga different mass-to-charge ration without adjusting the voltage of theelectron multiplier. In additional embodiments, the method comprisesscanning a range of ions of different mass-to-charge ratio withoutadjusting the gain of the electron multiplier. In certain embodiments,the method comprises calculating a sample concentration from thedetermined mean current. In other embodiments, the method comprisesdetermining the mean current by calculating the currents at selecteddynodes and discarding calculated currents below the noise currentsignal and above the saturation current signal, and scaling eachnon-discarded calculated current by its respective gain and averagingthe scaled currents to determine the mean current.

In an additional aspect, a method of measuring ions comprisingseparately controlling a bias voltage in each dynode of an electronmultiplier comprising a plurality of dynodes is provided. In someembodiments, the separately controlling the bias voltage in each dynodecomprises regulating the dynode voltage to be substantially constantwith increasing electron current and/or while allowing variableinput/output currents at each dynode. In other embodiments, the methodcomprises calculating currents (input currents or output currents) atselected dynodes of the plurality of dynodes, discarding calculatedcurrents below a noise current level and above the saturation currentlevel (or using current from dynodes which are above a minimum noisethreshold and below a maximum saturation threshold), scaling eachnon-discarded calculated current by its respective gain, and averagingthe scaled currents to determine a mean current.

In another aspect, a method of analyzing a sample comprising amplifyingan ion signal from the sample by independently measuring a current(input current or output current) at each of a plurality of dynodes ofan electron multiplier is provided. In certain examples, the methodcomprises calculating currents at each dynode of the plurality ofdynodes, discarding calculated currents below a noise current level andabove the saturation current level (or using current from dynodes whichare above a minimum noise threshold and below a maximum saturationthreshold), scaling each non-discarded calculated current by itsrespective gain, and averaging the scaled currents to determine a meancurrent.

In an additional aspect, a method of analyzing a sample comprisingamplifying an ion signal from the sample by independently measuring acurrent (input current or output current) at two or more of a pluralityof dynodes in an electron multiplier comprising a plurality of dynodesis described. In some examples, the method comprises calculatingcurrents at each of the two or more dynodes of the plurality of dynodes,discarding calculated currents below a noise current level and above thesaturation current level (or using current from dynodes which are abovea minimum noise threshold and below a maximum saturation threshold),scaling each non-discarded calculated current by its respective gain,and averaging the scaled currents to determine a mean current. In someembodiments, the method comprises measuring currents from every otherdynode of the plurality of dynodes.

In another aspect, a system comprising a plurality of dynodes, at leastone electrometer electrically coupled to one of the plurality ofdynodes, and a first processor electrically coupled to the at least oneelectrometer, the processor configured to determine a mean current (meaninput current or mean output current) from current measurements measuredby the electrometer is provided. In certain embodiments, the firstprocessor is configured to determine the mean current by calculatingcurrents at the at least one dynode of the plurality of dynodes,discarding calculated currents below a noise current level and above thesaturation current level (or using current from dynodes which are abovea minimum noise threshold and below a maximum saturation threshold),scaling each non-discarded calculated current by its respective gain,and averaging the scaled currents to determine a mean current. In otherembodiments, the system comprises a second electrometer electricallycoupled to a dynode other than the dynode electrically coupled to theelectrometer. In some embodiments, the processor is configured todetermine the mean input current by calculating input currents at thedynode electrically coupled to the electrometer and at the dynodeelectrically coupled to the second electrometer, discarding calculatedcurrents below a noise current level and above the saturation currentlevel (or using current from dynodes which are above a minimum noisethreshold and below a maximum saturation threshold), scaling eachnon-discarded calculated current by its respective gain, and averagingthe scaled currents to determine a mean current. In other embodiments,each of the plurality of dynodes is electrically coupled to a respectiveelectrometer. In additional embodiments, the processor is configured todetermine the mean current by calculating currents at each dynode of theplurality of dynodes, discarding calculated currents below a noisecurrent input level and above the saturation current level (or usingcurrent from dynodes which are above a minimum noise threshold and belowa maximum saturation threshold), scaling each non-discarded calculatedcurrent by its respective gain, and averaging the scaled currents todetermine a mean current.

Additional attributes, features, aspects, embodiments and configurationsare described in more detail herein.

BRIEF DESCRIPTION OF THE FIGURES

Certain features, aspects and embodiments of the signal multipliers aredescribed with reference to the accompanying figures, in which:

FIG. 1 is an illustration of a detector comprising a plurality ofdynodes, in accordance with certain examples;

FIG. 2 is an illustration of a detector where each dynode iselectrically coupled to an electrometer, in accordance with certainexamples; The processor is not connected to the dynode, allelectrometer's need to show an insulated connection to the processor,all electrometer's need to show a bias power supply connection.

FIG. 3 is an illustration of detector where every other dynode iselectrically coupled to an electrometer, in accordance with certainexamples; Same as above

FIG. 4 is an illustration of a detector where every third dynode iselectrically coupled to an electrometer, in accordance with certainexamples; Same as above

FIG. 5 is an illustration of a detector where every fourth dynode iselectrically coupled to an electrometer, in accordance with certainexamples; Same as above

FIG. 6 is an illustration of a detector where every fourth dynode iselectrically coupled to an electrometer, in accordance with certainexamples; Same as above

FIG. 7 is a chart showing a signal intensity range for each of aplurality of dynodes, in accordance with certain examples;

FIG. 8 is an illustration showing the use of a resistor ladder tocontrol the voltage of dynodes in a detector, in accordance with certainexamples;

FIG. 9 is an illustration showing the use of a plurality ofelectrometers each electrically coupled to a respective dynode, inaccordance with certain examples; Show insulated connections toprocessor

FIG. 10 is an illustration showing a power converter electricallycoupled to an amplifier to provide power to the amplifier, in accordancewith certain examples;

FIG. 11 is an illustration showing an example circuit configured toprovide separate control of the dynode bias voltages in a detector, inaccordance with certain examples;

FIG. 12 is a schematic of a circuit configured to terminateamplification of a signal in response to saturation of a dynode, inaccordance with certain examples;

FIG. 13 is a chart illustration showing the dynamic range of variousdynodes, in accordance with certain examples;

FIG. 14A is a circuit configured to control dynode voltage, inaccordance with certain examples;

FIGS. 14B and 14C together show a schematic of another circuitconfigured to control dynode voltage, in accordance with certainconfigurations;

FIG. 15 is an illustration of a side-on detector in accordance withcertain examples;

FIG. 16 is a block diagram of a mass spectrometer, in accordance withcertain examples;

FIG. 17A is an illustration of a microchannel plate, in accordance withcertain examples;

FIG. 17B is an illustration of stacked microchannel plates each of whichcan function as a dynode, in accordance with certain configurations;

FIG. 18 is an example of a camera, in accordance with certain examples;

FIG. 19 is an illustration of a system for performing Augerspectroscopy, in accordance with certain examples;

FIG. 20 is an illustration of a system for performing ESCA, inaccordance with certain examples; and

FIG. 21 is a simplified schematic of a continuous electron multiplier,in accordance with certain configurations.

It will be recognized by the person of ordinary skill in the art, giventhe benefit of this disclosure, that the components in the figures arenot limiting and that additional components may also be included withoutdeparting from the spirit and scope of the technology described herein.

DETAILED DESCRIPTION

Certain features, aspects and embodiments described herein are directedto ion detectors and systems using them that can receive incident ions,amplify a signal corresponding to the ions and provide a resultingcurrent or voltage. In some embodiments, the ion detectors and systemsdescribed herein can have an extended dynamic range, accepting largeelectron currents, without damaging or prematurely aging the device. Inother instances, the ion detectors and systems may be substantiallyinsensitive to overloading or saturation effects as a result of highconcentrations (or high amounts of ions emitted or otherwise provided tothe ion detector) while still providing rapid acquisition times andaccurate measurements.

In some embodiments, the dynodes of the ion detectors described hereincan be used to measure signals, e.g., signals representative of theincident ions, in a manner that does not overload the dynodes. Forexample, the detectors can be configured such that dynodes downstream ofa saturated dynode are “shorted out” or not used in the amplification.This configuration can increase the lifetime of the ion detectors andcan permit use of the ion detectors over a wide concentration range ofion current without having to alter or adjust the gain of the iondetectors for each sample. For example, the voltage (or current) of eachdynode can be monitored and/or used to measure the signal. If desired,dynodes that provide a signal above a noise level and/or below asaturation level can be monitored and grouped together, e.g., to providea mean signal that can be used to determine concentration, ions persecond or otherwise provide a desired output, e.g., an image, thatcorresponds to the incident light. Where dynode saturation is measured,signal amplification can be terminated at dynodes downstream of thesaturated dynode, or optionally at the saturated dynode itself, toenhance the lifetime of the ion detectors and systems. Reference to theterms “upstream” and “downstream” is understood to refer to the positionof one dynode relative to another dynode. For example, a dynode of adetector that is immediately adjacent to an entry aperture of thedetector would be upstream of a dynode that is immediately adjacent toan exit aperture of the detector. Similarly, a dynode that isimmediately adjacent to the exit aperture would be downstream of adynode that is immediately adjacent to the entry aperture.

In certain embodiments, the ion detectors and systems described hereinhave wide applicability to many different types of devices including,but not limited to, ion detectors of medical and chemicalinstrumentation, e.g., mass spectrometry, radiation detectors, Faradaycups, Geiger counters, scintillation counters and other devices whichcan receive ions and amplify ion signals to provide a current (orvoltage), image or signal representative of incident ions. The devicesmay be used with, or may include, one or more scintillators, primaryemitters, secondary emitters or other materials to facilitate iondetection and/or use of the ions to provide an image. Visual imagingcomponents can be used with the measured signals to construct imagesrepresentative of the ions received by the detectors and systemsdescribed herein. Examples of these and other ion detectors and systemsare described in more detail below.

Certain figures are described below in reference to devices includingdynodes or dynodes stages. It will be recognized by the person ofordinary skill in the art, given the benefit of this disclosure, thatthe exact number of dynodes or dynode stages can vary, e.g., from 5 to30 or any number in between or other numbers of dynode stages greaterthan 30, depending on the desired signal amplification, the desiredsensitivity of the device and other considerations. In addition, wherereference is made to channels, e.g., channels of a microchannel platedevice, the exact number of channels may also vary as desired. In someconfigurations, the dynodes may be present in a continuous dynodedevice.

In certain embodiments and referring to FIG. 1, certain components of anion detector 100 are shown. The detector 100 comprises an optionalcollector (or anode) 135 and a plurality of dynodes 125-133 upstream ofthe collector 135. While not shown, the components of the detector 100would typically be positioned within a tube or housing (under vacuum)and may also include a focusing lenses or other components to providethe ion beam 120 to the first dynode 126 at a suitable angle. In use ofthe detector 100, ion beam 210 is incident on the first dynode 126,which converts the ion signal into an electrical signal shown as beam122 by way of the photoelectric effect. In some embodiments, the dynode126 (and dynodes 127-133) can include a thin film of material on anincident surface that can receive ions and cause a correspondingejection of electrons from the surface. The energy from the ion beam 120is converted by the dynode 126 into an electrical signal by emission ofelectrons. The exact number of electrons ejected per ion depends, atleast in part, on the work function of the material and the energy ofthe incident ion. The secondary electrons emitted by the dynode 126 areemitted in the general direction of downstream dynode 127. For example,a voltage-divider circuit (as described below), or other suitablecircuitry, can be used to provide a more positive voltage for eachdownstream dynode. The potential difference between the dynode 126 andthe dynode 127 causes electrons ejected from the dynode 126 to beaccelerated toward the dynode 127. The exact level of accelerationdepends, at least in part, on the gain used. Dynode 127 is typicallyheld at a more positive voltage than dynode 126, e.g., 100 to 200 Voltsmore positive, to cause acceleration of electrons emitted by dynode 126toward dynode 127. As electrons are emitted from the dynode 127, theyare accelerated toward downstream dynode 128 as shown by beams 140. Acascade mechanism is provided where each successive dynode stage emitsmore electrons than the number of electrons emitted by an upstreamdynode. The resulting amplified signal can provided to the optionalcollector 135, which typically outputs the current to an externalcircuit through one or more electrical couplers of the ion detector 100.The current measured at the collector 135 can be used to determine theamount of ions that arrive per second, the amount of a particular ion,e.g., a particular ion with a selected mass-to-charge ratio, that ispresent in the sample or other attributes of the ions. If desired, themeasured current can be used to quantitate the concentration or amountof ions using conventional standard curve techniques. In general, thedetected current depends on the number of electrons ejected from thedynode 126, which is proportional to the number of incident ions and thegain of the device 100. Gain is typically defined as the number ofelectrons collected at the collector 135 relative to the number ofelectrons ejected from the dynode 126. For example, if 5 electrons areemitted at each dynode, and the device 100 includes 8 total dynodes,then the gain is 5⁸ or about 390,000. The gain is dependent on thevoltage applied to the device 100. For example, if the voltage isincreased, the potential differences between dynodes are increased,which results in an increase in incident energy of electrons striking aparticular dynode stage.

In some embodiments, the ion detector 100 can be overloaded bypermitting too many ions to be introduced into the housing and/or byadjusting the gain to be too high. As noted above, the gain of existingion detectors can be adjusted by changing or adjusting a control voltageto provide a desired signal without saturation of the detector. Forexample, the operating voltage of a typical detector may be between800-3000 Volts. Changing the operating voltage can result in a change inthe gain. Typical gain values may be from about 10⁵ to about 10⁸. Forany given gain, the detector has a useful dynamic range, which islimited by saturation at the high current end and detector noise in caseof low input current. The gain adjustment often takes place from sampleto sample to avoid overloading the detector at high sampleconcentrations (or high amounts of ions) and to avoid not providingenough signal amplification at low concentrations of sample (or lowlevels of incident ions). Alternatively, a gain can be selected (byselecting a suitable operating voltage) so that varying levels of ioncurrent at different mass-to-charge ratios do not saturate the detector.Adjusting the gain from measurement-to-measurement or image-to-imageincreases sampling time, can reduce detector response time and may leadto inaccurate results. Where the gain is too high, the detector canbecome overloaded or saturated, which can result in reduced lifetime forthe detector and provide substantially inaccurate measurements. Wherethe gain is too low, low levels of ions may go undetected. In certainembodiments described herein, the gain of the detector can be keptconstant and can be rendered insensitive to saturation or overloading athigh levels or the amounts of ions entering into the detector. Instead,the current to selected dynode stages can be measured, reflecting theion current difference of incoming electrons to leaving electrons. Thesereadings can be used to determine whether or not the electron currentshould be extracted at the next stage below, which can stop all electroncurrent flow to the lower dynodes, i.e. downstream dynodes. The measuredcurrent at selected dynode stages can be scaled by their stage gain andthen averaged or otherwise used to determine a mean input current signalthat is representative of the concentration or amount of ions thatarrives at the detector. Illustrations of such processes are describedin more detail below.

In certain embodiments, each of the dynodes 126-133 (and collectivelyshown as element 125) of the ion detector 100 can be configured toelectrically couple to an electrometer so that a current (input currentor output current) at each of the plurality of dynodes 125 can bemonitored or measured. In some configurations, the voltage differencebetween each dynode may be around 100 to 200V. As described elsewhereherein, the electrometer may part of an analog circuit or a digitalcircuit. For example, a solid-state amplifier comprising one or morefield-effect transistors can be used to measure the current at each ofthe plurality of dynodes 126-133. In some instances, each of theplurality of dynodes 126-133 may include a respective solid-stateamplifier. If desired, the amplifier can be coupled to one or moresignal converters, processors or other electrical components. Incombination, the components may provide or be considered amicrocontroller comprising one or more channels, e.g., ADC channels. Insome embodiments, a single microprocessor can be electrically coupled toone, two or more, e.g., all, of the dynodes such that current values cansimultaneously be provided to the processor for the one, two or more,e.g., all, dynodes. Because of the different dynode voltages, thecurrent values can be provided by way of some means of electricallyisolating the various signals from each dynode, e.g., optocouplers,inductors, light pipe, IRF devices or other components can be used. Forexample, each dynode/electrometer pair can be electrically isolatedand/or electrically insulated from other dynode/electrometer pairs suchthat separate signals can be measured from each of the dynodes. In otherconfigurations, a processor electrically coupled to suitable components(as described herein) can monitor current levels at each dynode and canbe used to determine a mean input current for determining aconcentration of a sample or for constructing an image based on thedetermined inputs.

In certain embodiments and referring to FIG. 2, one configuration ofcertain components in an ion detector system is shown. In FIG. 2, an iondetector 200 comprises a plurality of dynodes stages 230-237 and anoptional collector 220, where though the collector 220 can be omittedand the last dynode 237 may be the terminal dynode. In the detector 200,each of the dynode stages 230-237 is electrically coupled to arespective electrometer 240-247. The electrometers 240-247 can each beelectrically coupled to a first processor 250, e.g., through separateinput channels (not shown) of the processor 250. If desired, thecollector 220 can also be electrically coupled to an optionalelectrometer 252. In certain instances, it may be desirable to switchoperation of the detector 200 from the state where one or more internaldynode currents are monitored to a second state where only current atthe collector 237 is monitored. Even where a collector 220 is present,the collector is typically positioned so far downstream that currentoutput is measured upstream of the collector 220, e.g., current outputis measured at dynode 237 or a dynode upstream of dynode 237. As notedherein, the processor 250 may be present on a printed circuit board,which may include other components commonly found on printed circuitboards including, but not limited to, I/O circuits, data buses, memoryunits, e.g., RAM, clock generators, support integrated circuits andother electrical components. While not shown, the dynodes/electrometerpairs of the detector 200 may be electrically isolated from each otherto provide separate signals to the first processor 250.

In other embodiments and referring now to FIG. 3, it may not bedesirable to monitor the current at each dynode of the detector. Forexample, in an ion detector 300, every other dynode is electricallycoupled to an electrometer. The detector 300 comprises a plurality ofdynodes stages 330-337 and an optional collector 320, where thecollector 320 can be omitted and the last dynode 337 may be the terminaldynode. In the detector 300, every other dynode stage is electricallycoupled to a respective electrometer. For example, dynode stages 330-333are not electrically coupled to an electrometer, and each of dynodestages 334-337 is electrically coupled to a respective electrometer344-347. The electrometers 344-347 can each be electrically coupled to afirst processor 350. If desired, the collector 320 can also beelectrically coupled to an optional electrometer 352 and may include aseparate electrical coupling to the processor 350. As noted herein, theprocessor 350 can be present on a printed circuit board, which mayinclude other components commonly found on printed circuit boardsincluding, but not limited to, I/O circuits, data buses, memory units,e.g., RAM, clock generators, support integrated circuits and otherelectrical components. By configuring the detector with an electrometeron every other electrode, detector fabrication and reduced circuitry canbe implemented. As noted in more detail below, selected currents, e.g.,selected input currents, from the detector 300 can be used to determinea mean input current, which can be used for calculating an ionconcentration, reconstructing an image or for other means. While theconfiguration shown in FIG. 3 illustrates an electrometer being presentat every other dynode, it may be desirable to include an electrometer onadjacent dynodes followed by a dynode stage without an electrometerrather than spacing the electrometers on an every other dynode basis.For example, where a detector comprises eight dynodes and fourelectrometers, it may be desirable to omit electrometers from all stagesexcept the final four dynode stages 332, 333, 336 and 337. While notshown, the dynodes/electrometer pairs of the detector 300 may beelectrically isolated from each other to provide separate signals to thefirst processor 350.

In additional embodiments and referring to FIG. 4, it may be desirableto configure the detector with an electrometer on every third dynode.For example, a detector 400 comprises a plurality of dynodes 430-437 andan optional collector 420, where the collector 420 can be omitted andthe last dynode 437 may function as a collector. In the detector 400,every third dynode stage is electrically coupled to a respectiveelectrometer. For example, each of dynode stages 434, 432 and 437 iscoupled to an electrometer, 444, 442 and 447, respectively, and allother dynode stages are not coupled to an electrometer. Theelectrometers 444, 442 and 447 can each be electrically coupled to afirst processor 450, e.g., through separate input channels (not shown)of the processor 450. If desired, the collector 420 can also beelectrically coupled to an optional electrometer 452. While threeelectrometers are shown as being present in the detector 400, the threeelectrometers could, if desired, be positioned together in the middle ofthe dynode stages, together toward one end of the dynode stages orspaced in some other manner than every third dynode. For example, it maybe desirable to omit electrometers from all stages except the finalthree dynode stages 433, 436 and 437. Additional configurations of adetector comprising three electrometers each electrically coupled to arespective dynode will be readily selected by the person of ordinaryskill in the art, given the benefit of this disclosure. While not shown,the dynodes/electrometer pairs of the detector 400 may be electricallyisolated from each other to provide separate signals to the firstprocessor 450.

In other embodiments and referring to FIG. 5, it may be desirable toconfigure the detector with an electrometer on every fourth dynode. Forexample, a detector 500 comprises a plurality of dynodes 530-537 and anoptional collector 520, where the collector 520 can be omitted and thelast dynode 537 may function as a collector. In the detector 500, everyfourth dynode stage is electrically coupled to a respectiveelectrometer. For example, each of dynode stages 535 and 537 is coupledto an electrometer, 545 and 547, respectively, and all other dynodestages are not coupled to an electrometer. The electrometers 545 and 552can each be electrically coupled to a first processor 550, e.g., throughseparate input channels (not shown) of the processor 550. If desired,the collector 520 can also be electrically coupled to an optionalelectrometer 552. While two electrometers are shown as being present inthe detector 500, the two electrometers could, if desired, be positionedtogether in the middle of the dynode stages, together toward one end ofthe dynode stages or spaced in some other manner than every fourthdynode. For example, it may be desirable to omit electrometers from allstages except the final two dynode stages 533 and 537. Additionalconfigurations of a detector comprising two electrometers eachelectrically coupled to a respective dynode will be readily selected bythe person of ordinary skill in the art, given the benefit of thisdisclosure. While not shown, the dynodes/electrometer pairs of thedetector 500 may be electrically isolated from each other to provideseparate signals to the first processor 550.

In some examples, it may be desirable to configure the detector with anelectrometer on every fifth dynode. For example and referring to FIG. 6,a detector 600 comprises a plurality of dynodes 630-637 and an optionalcollector 620, where the collector 620 can be omitted and the lastdynode 637 may function as a collector. In the detector 600, every fifthdynode stage is electrically coupled to a respective electrometer. Forexample, each of dynode stages 633 and 634 is coupled to an electrometer643 and 644, respectively, and all other dynode stages are not coupledto an electrometer. The electrometers 643 and 644 can each beelectrically coupled to a first processor 650, e.g., through separateinput channels (not shown) of the processor 650. If desired, the anode620 can also be electrically coupled to an optional electrometer 652.While two electrometers are shown as being present in the detector 600,the two electrometers could, if desired, be positioned together in themiddle of the dynode stages, together toward one end of the dynodestages or spaced in some other manner than every fifth dynode. Inaddition, the electrometer coupling need not occur on the second andseventh dynode stages 634 and 633, respectively, but instead may bepresent on the first dynode 630 and sixth dynode 636, the third dynode631 and the eighth dynode 637 or other dynodes spaced apart by fourdynode stages. While not shown, the dynodes/electrometer pairs of thedetector 600 may be electrically isolated from each other to provideseparate signals to the first processor 650.

While FIGS. 2-6 show particular electrometer spacing, where more thaneight dynode stages are present, the spacing may be different than theparticular spacing shown in FIGS. 2-6. For example, the spacing may begreater than every fifth dynode where more than eight dynodes arepresent, may be concentrated toward the middle dynode stages, may beconcentrated toward dynode stages near the anode or may otherwise bespaced in a desired or selected manner. In some instances where atwenty-six dynode electron multiplier is used, a first electrometer maybe present at a mid-point, e.g., electrically coupled to dynode 13, anda second electrometer can be positioned upstream of dynode 13 ordownstream of dynode 13.

In certain embodiments, in operation of the detectors and systemsdescribed herein, the signal, e.g., input or output current, can bemonitored at the various dynode stages, e.g., this current will be aninput current if the next dynode is positively biased or an outputcurrent otherwise. This signal can be used to determine a mean ioncurrent signal, which may be used for qualitative purposes, quantitativepurposes or used in image construction. Referring to the schematic shownin FIG. 7, illustrative signal values for a detector comprising twelvedynode stages is shown. The bars for each dynode represent the dynamicrange of each of the dynodes. For exemplary purposes, dynode 1 isconsidered to be the dynode immediately adjacent to and downstream of anentry aperture where ions enter into the detector. A lower signal limit710 can be selected by the processor such that an output signal belowthe lower limit is considered to be within the noise, e.g., has asignal-to-noise ratio of less than 3. These signals can be discarded.Similarly, an upper signal limit 720 can be selected where values abovethe upper limit are considered to be saturated dynodes. These values canalso be discarded by the processor. Additionally, as described below,where a saturated dynode is detected, dynodes downstream of thesaturated dynode can be shorted out, making the saturated dynodefunction as a collector plate to pull out all electrons to protect thedetector. No signals are shown in FIG. 7 for dynodes 11 and 12 as thosedynodes are downstream of the saturated dynode (dynode 10). Theremaining values within the selected current window (signals for dynodes3-9) can be used to determine a mean ion signal. For example, if theoutput current is monitored and the gain of the dynode stages is known,then a mean signal can be determined for the various dynode stages usingthe current and the gain values. Alternatively, the input current ateach dynode can be measured and converted simultaneously. For example,the input current can be computed at each dynode using the gain curve ofthe dynodes. The input currents (for all input current below saturateddynodes and input currents above dynodes above the signal-to-noise) cansimultaneously be averaged, e.g., after normalizing each using the gain,to determine a mean input current that corresponds to the ion signalincident on the ion detector. Additionally, the detector can beconfigured to shut down dynodes where saturation is observed. Forexample, if saturation is observed at any dynode stage, then that dynodestage and/or subsequent downstream dynode stages can be shut down, e.g.,by altering the voltage at downstream dynodes to stop the cascade, toprotect the remaining dynodes of the detector, which will extenddetector lifetimes. The averaging of signals and monitoring ofindividual dynodes can be performed in real time to extend the dynamicrange of the detectors, e.g., the dynamic range can be extended by thegain.

In certain embodiments and referring to FIG. 8, a conventional schematicof certain components of a detector are shown. Six dynodes 810-815 ofthe detector 800 are shown, though as indicated by the curved linesbetween dynodes 812 and 813 additional dynode stages can be present. Aresistor ladder 830 is used to electrically bias downstream dynodes tohave a more positive voltage than upstream dynodes, which results inacceleration of electrons and amplification of the ion signal 805. Forexample, the voltage of the first dynode 810 is selected such thatelectrons striking the dynode 810 will be ejected and accelerated towardthe second dynode 811. The bias voltage of the various dynodes 810-815is achieved by selecting suitable resistor values in the resistor ladder830. For example, the resistor values are selected to supply thedifference between the input current minus the output current for eachdynode, while substantially maintaining the bias voltage. As shown inFIG. 8, an amplifier 840, e.g., an amplifier with feedback, that iselectrically coupled to an analog-to-digital converter 850 can bepresent to send digital signals to a processor (not shown) for measuringthe current at the dynode 815.

In certain configurations of the detectors described herein, thesupplied current to each dynode can be a direct measure of the electroncurrent. An electrometer can be used to measure the input current ateach dynode without disturbing or altering the other dynode stages.Generally, an amplifier can be coupled to each dynode bias voltage tocreate a virtual ground at the bias voltage. The output voltage withrespect to the virtual ground is proportional to the dynode currentmultiplied by the resistance of the feedback resistor. Each signal fromthe amplifier can then be converted, e.g., using an analog-to-digitalconverter, and the resulting values can be provided to a processorthrough some means of electrical insulation (or electrical isolation orboth) for use in determining a mean input or output current from thosesignals below a saturation level and above a noise level. Oneillustration of such a configuration is shown in FIG. 9 where threedynode stages are shown for representative purposes. A dynode 911 isshown as being electrically coupled to an amplifier 921 and a signalconverter 931. A resistor 941 is electrically coupled to the amplifier921. The amplifier 921 is coupled to the dynode bias voltage of dynode911 to create a virtual ground at the bias voltage. The dynode biasvoltage can be provided using resistor ladder 905 as described, forexample, in reference to the resistor ladder of FIG. 8. The outputvoltage with respect to the virtual ground is proportional to thecurrent from the dynode 911 multiplied by the resistance of the feedbackresistor 941. The output from the amplifier 921 can then be converted bysignal converter 931, and the resulting value can be provided to aprocessor 950 for use in determining a mean input current if the signalfrom the dynode 911 is within an acceptable signal window, e.g., iswithin a window or range between a saturation level signal and a noiselevel signal. The input current (or output current) at dynode 912 mayalso be measured in a similar way. In particular, an amplifier 922 iselectrically coupled to the dynode 912 and to a signal converter 932. Aresistor 942 is electrically coupled to the amplifier 922. The amplifier922 is coupled to the dynode bias voltage of dynode 912 to create avirtual ground at the bias voltage. The output voltage with respect tothe virtual ground is proportional to the current from the dynode 912multiplied by the resistance of the feedback resistor 942. The outputfrom the amplifier 922 can then be converted by signal converter 932,and the resulting value can be provided to the processor 950. Thecurrent may be measured at dynode 913 in a similar way using theamplifier 923, the signal converter 933, the feedback resistor 943 andthe processor 950. If desired, separate digital signals can be providedsuch that measured currents within an acceptable window comprise wordsor signals that are used by a processor to determine a mean inputcurrent, and signals that are not acceptable, e.g., within the noise orrepresentative of saturated signals, are coded differently, e.g., havedifferent words or signals, and are not used by the processor in thecalculation.

In certain examples, while all three dynodes in FIG. 9 are shown asincluding a respective electrometer, it may be desirable to include onlytwo electrometers, e.g., the current at dynode 912 may not be monitored.In some embodiments described herein, the detectors and system caninclude two, three, four, five or more electrometers coupled to internaldynodes, e.g., those between a first dynode and a collector, to providesufficient signals in determining mean input signals. If desired, eachinternal dynode can include a respective electrometer to increase theoverall accuracy of the measurements. Referring to FIG. 10, a singledynode 1010 is shown as being electrically coupled to an amplifier 1020.The amplifier 1020 floats at the bias voltage of the dynode 1010. Afloating DC/DC converter 1030 can be electrically coupled to theamplifier 1020 and a signal converter 1040 to provide power to thesecomponents. The DC/DC converter 1030 typically converts a highervoltage, e.g., 24 Volts, to a lower voltage, e.g., 5 Volts, that isprovided to the amplifier 1020 and the signal converter 1040. Powerconverters other than DC/DC converters may also be used in theconfiguration shown in FIG. 10 to provide power to the electrometer. Ifdesired, each dynode can be electrically coupled to a power converter.In some embodiments, only those dynodes electrically coupled to anelectrometer are also electrically coupled to a power converter. Ifdesired, the first dynode 1010 can be held at a fixed offset, which canassist in keeping the ion to electron conversions constant.

In certain examples, the dynode bias voltage, as described herein, canbe provided by selecting suitable resistors in the resistor ladder. Inthis configuration, changing the input ion current will change thedynode to dynode voltage and can introduce errors. To avoid this error,it may be desirable to regulate each dynode voltage to reduce any errorsthat may be introduced from voltage changes with increased electroncurrents. One configuration that permits controlling the dynode voltagesseparately is shown in FIG. 11. To achieve a substantially constantvoltage, a Zener diode or a regulated amplifier can be used. The deviceof FIG. 11 includes dynodes 1110 and 1111 electrically coupled toamplifiers 1120 and 1121, respectively, similar to the configurationdescribed in reference to FIG. 10. An amplifier 1131 can be electricallycoupled to the resistor ladder 1105 and to a Zener diode 1141 to providefor independent control of the voltage provided to the dynode 1110. Forexample, the Zener diode 1141 is electrically coupled to an input of theamplifier 1131 to provide for additional control of the bias voltage forthe dynode 1110, e.g., to limit or clip the voltage if desired or neededand generally aid in providing a bias voltage to the dynode 1110 thatdoes not vary substantially as electron currents increase at otherdynodes of the detector. Similarly, a Zener diode 1142 is electricallycoupled to an input of an amplifier 1132 to permit control of the biasvoltage to dynode 1111. An electrometer can be electrically coupled toeach of the dynodes 1110 and 1111. For example, an amplifier 1120 can beelectrically coupled to the dynode 1110 and used to provide a signal toa signal converter 1150, which may convert the signal, e.g., to adigital signal, and provide the converted signal to a processor (notshown). Similarly, an amplifier 1121 can be electrically coupled to thedynode 1111 and used to provide a signal to a signal converter 1151,which may convert the signal, e.g., to a digital signal, and provide theconverted signal to a processor (not shown). Where the detector includesmore than two dynodes, there can be multiple voltage controllers, e.g.,similar to the amplifier/Zener diode combination shown in FIG. 11,between dynodes to separately control the dynode to dynode voltage ofthe detector. Each dynode can provide a signal to the processor separatefrom the signals sent by other dynodes. If desired, there need not bevoltage control between each dynode node. For example, it may bedesirable to omit voltage control between certain dynodes to simplifythe overall construction of the detector. In the configuration shown inFIG. 11, the resistor chain can use very low current, e.g., less than0.1 mA, which reduces generated heat and current demand on the detectorpower supply, which is typically a 3 kV power supply.

In certain embodiments, at high levels of incident ions, the downstreamdynodes, e.g., those closer to where a collector would typically befound, may begin to saturate. For example, as the input currentincreases, the downstream dynode stages will start to saturate theamplifiers and the signal converters. While the electronics are notlikely to be damaged from saturation, current to these dynodesincreases, producing heat in the resistor ladder or voltage regulators.In addition, the materials present on the dynode surfaces that ejectelectrons can be damaged. Damage or deterioration of the dynode surfacecan result in a change in the local gain of a particular dynode, whichcan lead to measurement errors. Desirably, the dynode voltages areselected to overlap well with the dynamic range of each electrondetector. It is desirable, for example, to overlap more than 50% toachieve a linear output. Where such a gain is selected for a certain ionlevel and a subsequent measurement is performed where more ions of acertain mass-to-charge ratio are incident, it may be desirable to stopthe electron beam next to a saturated dynode. In some embodiments, thesaturated dynode may be the last dynode where the signal is amplified,e.g., the saturated dynode may function as a collector, whereas in otherexamples, a dynode downstream of the saturated dynode can be shorted outto act like a collector plate to remove all electrons. Many differentmechanisms can be used to terminate signal amplification. In oneembodiment, the bias voltage of a dynode adjacent to and downstream of asaturated dynode can be adjusted such that electrons are not acceleratedfrom the saturated dynode toward the adjacent downstream dynode, whichwould cause the saturated dynode to function as a collector plate. Inthis manner, the electron stream is terminated at the saturated dynode.

Referring to FIG. 12, a schematic is shown of a circuit that can beimplemented to terminate signal amplification in the detectors andsystems described herein. The components not labeled in FIG. 12 aresimilar to those described and shown in reference to FIG. 11. At thesaturation level, a downstream dynode 1211 (downstream relative to asaturated dynode 1210) can be biased slightly positive in respect to thesaturated dynode 1210. For example, the node can shorten the voltagedivider on the dynode stage below, to +5V node of the saturation dynode.If a reference voltage of about 2 Volts is present, the dynode 1211below will end up about +3V over the saturated dynode. The output signalof the saturated dynode will become a collector and will collect allelectron currents. The ADC will saturate in the reverse polarity. Ifdesired, this configuration can be used to clamp the dynode gain voltagedirectly, or can be detected by the control system. For example, as theincident signal changes, the particular dynode where signal terminationoccurs may change from measurement to measurement. Desirably, theprotection switching speed can be close to the ADC conversion speed, sosignal termination can be implemented before any damage to downstreamdynodes can occur.

It is a substantial attribute of embodiments described herein that bystopping the signal amplification at a saturated dynode (or a dynodedownstream from a saturated dynode), the gain of the device can be fixedand not user adjustable. For example, in a detector operated at a fixedgain and with 26 dynodes, if saturation is detected at dynode 23, thenamplification may be terminated by shorting out the amplification atdynode 23. For a subsequent measurement or receipt of ions with a sameor different mass-to-charge ratio at the same fixed gain, the number ofions may be such that saturation occurs at dynode 19. Amplification canbe terminated at dynode 19 without having to adjust the gain, as wouldbe required when using a typical electron multiplier. In this manner, asingle fixed gain can be selected, and the detector can monitor theinput currents of the dynodes to determine when signal amplificationshould terminate. One result of such configurations is extending thedynamic range of the detector without loss of linearity or detectionspeed. For example, if the current at each dynode is measured, then thedynamic range is extended by the gain. If a 16-bit analog-to-digitalconverter is used, then this is 65 k (2¹⁶) times the gain. Where thesystem is designed to terminate amplification at a saturated dynode, thedetector can be operated at a maximum voltage, e.g., 3 kV, to provide amaximum gain. At this voltage, a gain of 10⁷ would be anticipated inmany detectors. To account for noise and assuming a signal-to-noise of10:1 for a single ion event, the dynamic range would be reduced by afactor of 10. The total dynamic range when using a 16-bit ADC on everydynode would be expected to be about 6×10¹⁰ (65,000 times 10⁶). Ifconversion of the readings occurs at a frequency of 100 kHz, then about100,000 different sample measurements can be averaged to expand thedynamic range to a total dynamic range of about 6×10¹⁵. For a particularsample, different mass-to-charge ions varying greatly in intensities canbe scanned and detected without having to alter the gain of thedetector.

In certain embodiments to demonstrate a typical output of dynodes, andaccounting for the dynamic range at each dynode, an illustration isshown in FIG. 13 of the dynode current for each dynode in a 13 dynodedetector relative to an input current. As shown in FIG. 13, the outputof the ADC's for Dynodes 1 and 2 is very low and within the electronicnoise. As such, these outputs are discarded and not considered in theinput calculations. Dynodes 3 to 10 provide ADC outputs within anacceptable window. The signal values of dynodes 3-10 can be averaged toprovide a seven-fold accuracy improvement over a single ADC reading.Dynode 11 is measured as being saturated, which results in switching offof dynodes 12 and 13 thus terminating the amplification at dynode 11.The measurement from dynodes 11-13 can also be discarded or otherwisenot used in averaging to provide a mean input current that correspondsto an incident ion signal.

In certain examples and as described herein, measurement of a current atevery dynode is not required. Instead, every second, third or fourthdynode could be measured and used. The gain between each stage can beany value, and can be ‘calibrated’ by comparing its ADC reading to thestage below and above. This found gain can then be used as input currentequals the sum of all stage gains time ADC readings. In some instances,the fixed voltage can be larger than the sum of all dynode stagevoltages, and the bottom or last resistor can be used to absorb anyextra voltage. In addition, the bottom resistor can also absorb anyexcess voltage generated by shorting a dynode for termination of signalamplification. In some configurations, it may be desirable to haveenough dynodes to compensate for eventual aging. For example, if EM gaindecreases over time due to deterioration of surface materials, thesaturation point may move further downstream in the dynode set. If thelast dynode does not produce a signal-to-noise of 10 to 1 (or otherselected signal-to-noise) for a single ion event, that response may beindicative that the detector has exceeded its useful life. The expecteddetector lifetime should be much larger than the current conventionalsystem due to signal termination at a saturated dynode and protection ofdownstream dynodes.

In certain embodiments, another schematic of a circuit that can be usedto measure the signal from a dynode is shown in FIG. 14A. The circuit1400 generally comprises an amplifier 1410 electrically coupled to acapacitor 1420 and a controller 1405 (or processor if desired). Thecircuit is electrically coupled to a dynode (not shown) throughcomponent 1430. Digital signals can be provided from a processor andused to control the bias voltage of the dynodes. For example, signalsfrom the processor can be used to short out the dynode, to regulate thedynode bias voltage or to otherwise assist in the signal amplificationmechanism or terminate the signal amplification mechanism.

In certain configurations, another schematic of a circuit is shown inFIGS. 14B and 14C. The circuit has been split into two figures toprovide for a more user friendly version of the circuit. In theschematic NGND represent a virtual ground. The circuit comprises a DC/DCconverter U6 electrically coupled to amplifiers U16A and U16B to providea voltage to the dynode (labeled as node) of about 101 Volts. Areference voltage of about 4.096 volts is provided from a voltagereference U19 and can be used with the voltage from the DC/DC converterU6, e.g., using the outputs of amplifiers U16A and U16B and amplifierQ3, to provide the 101 Volts to the dynode. Analog signals from thedynode can be measured by an electrometer J4 and provided to ananalog-to-digital converter U12. The analog-to-digital converter U12 iselectrically coupled to digital isolators U23 and U24, which can isolatethe signals from the dynode. The outputted signals from each dynode canbe electrically insulated from the signals of other dynodes so that eachsignal from each dynode is separate from signals from other dynodes,which permits simultaneous measurement of signals from differentdynodes. To determine if a saturation signal is present at any onedynode, saturation threshold values can be set in software, and wheresaturation is detected at the dynode, the voltage can be clamped to stopamplification at the saturated dynode. For example, drive amplifier Q6and other components of the clamp can be used to short out the dynode,e.g., to place it at virtual ground NGND, which will stop signalamplification at that dynode. Each dynode of the dynode set may comprisea circuit similar to that shown in FIGS. 14B and 14C to provide forindependent voltage control, independent voltage clamping (if desired)and to provide separate, electrically isolated signals from eachnon-shorted dynode to a processor or other input device. In use of thecircuit of FIGS. 14B and 14C, dynode signals from dynodes of a dynodeset can be measured or monitored. Where a non-saturated signal isdetected, amplification may continue using downstream dynodes, e.g., byproviding a suitable voltage to the downstream dynodes. When asaturation signal is detected, the dynode where the saturation signal isobserved can be grounded to the virtual ground to terminate theamplification at that saturated dynode. Signals from dynodes downstreamof the clamped, saturated dynode generally represent noise signals as noamplification occurs at these downstream dynodes. Signals upstream ofthe saturated dynode and signals above a noise threshold value can beused, e.g., averaged, to determine a mean input current (or mean outputcurrent).

In certain embodiments, in implementing the detectors described herein,commercially available components can be selected and assembled as partof larger circuitry on a printed circuit board and/or as a separateboard or chip that can be electrically coupled to the dynodes. Certaincomponents can be included within the vacuum of the detectors, whereasother components may remain outside the vacuum tube of the detector. Forexample, the electrometers, over-current protections and voltagedividers can be placed into the vacuum tube as they do not produce anysubstantial heat that may increase dark current. To provide anelectrical coupling between the components in the vacuum tube and theprocessor of the system, suitable couplers and cabling, e.g., a flex PCBfeed cable that can plug into a suitable coupler, can be implemented.

In certain embodiments, the detectors described herein can be configuredas either side-on or end-on (also referred to as head-on) devices.Examples of end-on devices are pictorially shown in FIGS. 1-4, forexample, where the light is incident on an end of the detector. Thehousing of an end-on detector would typically be opaque such that theend of the detector near the photocathode is the only portion thatreceives any substantial light. In other configurations, a side-ondetector can be implemented in a similar manner as described herein,e.g., a side-on detector can include a plurality of continuous dynodeswith one, two, three or more (or all) of the dynodes electricallycoupled to a respective electrometer. One illustration of a side-ondetector is shown in FIG. 15. The detector 1500 comprises an aperture1510, which is positioned on the side 1515 of the device 1500. Ions(shown as beam 1505 outside the detector and beam 1516 inside thedetector) can enter the aperture 1510 on the side 1515 of the detector1500 and strike a dynode 1520. As described in reference to the end-ondevice, the dynode 1520 can emit electrons which are amplified bydynodes 1521-1526 within the device 1500 and collected by the collector1530. Selected dynodes of the side-on detector 1500 can be electricallycoupled to a respective electrometer and may include suitable circuitry,e.g., similar to that described in connection with FIGS. 1-12, to permitmeasurement of input current at the dynodes 1520-1526 and calculation ofa mean input current signal, if desired. While an incident ion is shownin FIG. 15 as being incident at about a ninety degree angle relative tothe aperture 1510, angles other than ninety degrees can also be used. Ifdesired, one or more ion lens elements can be used to provide the ionsat a selected trajectory to the detector 1500.

In certain examples, the exact dynode configuration present in anydetector can vary. For example, the dynode arrangement may be of themesh type, Venetian blind type, linear-focused type, box-and-grind type,circular-cage type, microchannel plate type, metal channel dynode type,electron bombardment type or other suitable configurations. In certainembodiments, the detectors described herein can be produced usingsuitable materials for the dynode and the collector. For example, thedynodes can include one or more of the following elements or materials:Ag—O—Cs, GaAs:Cs, GaAs:P, InGaAs:Cs, Sb—Cs, Sb—K—Cs, Sb—Rb—Cs,Na—K—Sb—Cs, Cs—Te, Cs—I, InP/InGaAsP, InP/InGaAs, or combinationsthereof. The dynodes of the detectors may include one or more of carbon(diamond), AgMg, CuBe, NiAl, Al₂O₃, BeO, MgO, SbKCs, Cs₃Sb, GaP:Cs orother suitable materials. As noted herein, the exact material selectedfor use in the dynodes has a direct effect on the gain, and gain curvesfor a known material can be used in the calculations described herein ifdesired. One or more of these materials can be present on a surface at asuitable angle to permit the surface to function as a dynode. Thecollector may also include suitable materials to permit collection ofany electrons, e.g., one or more conductive materials.

In certain examples, the detectors described herein can be used in manydifferent applications including, but not limited to, medical andchemical instrumentation, ion and particle detectors, radiationdetectors, microchannel plate detectors and in other systems where itmay be desirable to detect ions or particles. Illustrations of these andother detectors are described in more detail below.

In certain embodiments, the detectors and associated circuitry describedherein can be used in medical and chemical instrumentation. For example,the detectors can be used in mass spectrometry applications to detections that result from fragmentation or ionization of a sample to beanalyzed. A general schematic of a mass spectrometer 1600 is shown inFIG. 16. The mass spectrometer 1600 comprises four general components orsystems including a sample introduction device 1610, an ionizationdevice 1620 (also referred to as an ion source), a mass analyzer 1630and a detector 1640. Each of these components is discussed in moredetail herein, but generally the detector 1640 may be any one of more ofthe detectors described herein, e.g., a detector comprising dynodeselectrically coupled to electrometers. As noted herein, the detector canmeasured the charge induced or the current produced when an ion isincident on the detector. The sample introduction device 1610, theionization device 1620, the mass analyzer 1630 and the detector 1640 maybe operated at reduced pressures using one or more vacuum pumps. Incertain examples, however, only the mass analyzer 1630 and the detector1640 may be operated at reduced pressures. The sample introductiondevice 1610 may take the form of a sample inlet system that can receivesample while permitting the components to remain under vacuum. Thesample introduction device 1610 can be configured as batch inlet, adirect probe inlet, a chromatographic inlet or other sample introductionsystems such as those used, for example, in direct sample analysis. Inbatch inlet systems, the sample is externally volatized and “leaks” intothe ionization region. In direct probe inlet systems, the sample isintroduced into the ionization region using a sample holder or probe. Inchromatographic inlet systems, the sample is first separated using oneor more chromatographic techniques, e.g., gas chromatography, liquidchromatography or other chromatographic techniques and the separatedcomponents then be introduced into the ion source 1620. In someembodiments, sample introduction device 1610 may be an injector, anebulizer or other suitable devices that may deliver solid, liquid orgaseous samples to the ionization device 1620. The ionization device1620 may be any one or more of the devices which can atomize and/orionize a sample including, for example, plasma (inductively coupledplasmas, capacitively coupled plasmas, microwave-induced plasmas, etc.),arcs, sparks, drift ion devices, devices that can ionize a sample usinggas-phase ionization (electron ionization, chemical ionization,desorption chemical ionization, negative-ion chemical ionization), fielddesorption devices, field ionization devices, fast atom bombardmentdevices, secondary ion mass spectrometry devices, electrosprayionization devices, probe electrospray ionization devices, sonic sprayionization devices, atmospheric pressure chemical ionization devices,atmospheric pressure photoionization devices, atmospheric pressure laserionization devices, matrix assisted laser desorption ionization devices,aerosol laser desorption ionization devices, surface-enhanced laserdesorption ionization devices, glow discharges, resonant ionization,thermal ionization, thermospray ionization, radioactive ionization,ion-attachment ionization, liquid metal ion devices, laser ablationelectrospray ionization, or combinations of any two or more of theseillustrative ionization devices. The mass analyzer 1630 may takenumerous forms depending generally on the sample nature, desiredresolution, etc. and exemplary mass analyzers are discussed furtherbelow. The detector 1640 may be any suitable detector described herein,e.g., electron multipliers, scintillation detectors, etc. any of whichmay comprise dynodes electrically coupled to electrometers. The system1600 is typically electrically coupled to a processor (not shown) whichincludes a microprocessor and/or computer and suitable software foranalysis of samples introduced into MS device 1600. One or moredatabases may be accessed by the processor for determination of thechemical identity of species introduced into MS device 1600. Othersuitable additional devices known in the art may also be used with theMS device 1600 including, but not limited to, autosamplers, such asAS-90plus and AS-93plus autosamplers commercially available fromPerkinElmer Health Sciences, Inc.

In certain embodiments, the mass analyzer 1630 of system 1600 may takenumerous forms depending on the desired resolution and the nature of theintroduced sample. In certain examples, the mass analyzer is a scanningmass analyzer, a magnetic sector analyzer (e.g., for use in single anddouble-focusing MS devices), a quadrupole mass analyzer, an ion trapanalyzer (e.g., cyclotrons, quadrupole ions traps, orbitraps),time-of-flight analyzers (e.g., matrix-assisted laser desorbedionization time of flight analyzers), and other suitable mass analyzersthat may separate species with different mass-to-charge ratios. In someembodiments, the mass analyzer may be coupled to another mass analyzerwhich may be the same or may be different. For example, a triplequadrupole device can be used as a mass analyzer. If desired, the massanalyzer 1630 may also include ions traps or other components that canassist in selecting ions with a desired mass-to-charge ratio from otherions present in the sample. The mass analyzer 1630 can be scanned suchthat ions with different mass-to-charge ratios are provide to thedetector 1640 in real time.

In certain embodiments, the detector 1640 selected for use may depend,at least in part, on the ionization technique and/or the mass analyzerselected. For example, it may be desirable to use an electron multipliercomprising dynodes coupled to electrometers with high dynamic range timeof flight analyzers and for instruments including quadrupole analyzers.In general, the detector 1640 may be any of the detectors describedherein including those with a plurality of dynodes, those withmultichannel plates and other types of detectors that can amplify an ionsignal and detect it as described herein. For example, the detector canbe configured as described in reference to FIGS. 1-12. In otherembodiments, certain components of the detectors described herein can beused in a microchannel plate to amplify a signal. The microchannel platefunctions similar to the dynode stages of the detectors described hereinexcept the many separate channels which are present provide spatialresolution in addition to amplification. The exact configuration of themicrochannel plate can vary, and in some examples, the microchannelplate (MCP) can take the form of a Chevron MCP, a Z-stack MCP or othersuitable MCPs. Illustrative MCPs are described in more detail below.Notwithstanding the type of detector used, the detector can receive ionsas the instrument scans different mass-to-charge ratios. A mass spectrumcan be produced which is a function of the number of ions having aselected mass-to-charge ratio for each of the mass-to-charge ratiosscanned. If desired, the number of ions arriving per second at aparticular mass-to-charge may be calculated. Depending on the level ofthe ions in a sample, the detector can dynamically determine whethersaturation at any particular dynode is present and use selected dynodeinput current to determine a mean input current for each ion. The meaninput current may be used to generate a mass spectrum that may be moreprecise than mass spectra generated using existing methods andtechniques.

In certain embodiments and referring to FIG. 17A, a schematic of amicrochannel plate 1700 is shown comprising a plurality of electronmultiplier channels 1710 oriented substantially parallel to each other.The exact number of channels in the plate 1700 can vary, e.g., 100-200or more. The MCP can include electrodes 1720 and 1730 on each surface ofthe plate to provide a bias voltage from one side to the other to sideof the plate. The walls of each of the channels 1710 can include amaterial which can emit secondary electrons that can be amplified downthe channel. Each channel (or a selected number of channels) can beelectrically coupled to a respective electrometer to measure the inputcurrent from each channel. For example, non-saturated channels can beused to calculate input currents and saturated channels can be shortedout to protect the channel or otherwise not used to provide a signal oran image. If desired, the electrodes 1720 and 1730 can be configured asan electrode array with an electrode corresponding to each channel topermit independent control of the voltage provided to each channel. Inaddition, in some configurations each channel can be electricallyisolated from other channels to provide a plurality of continuous butseparate dynodes in the plate 1700. An external voltage divider can beused to apply a bias voltage to accelerate electrons from one side ofthe device to the other. In certain embodiments, the MCP's can beconfigured as a chevron (v-like shape) MCP. In one configuration, achevron MCP includes two microchannel plates where the channels arerotated about ninety degrees from each other. Each channel of thechevron MCP can be electrically coupled to a respective electrometer ora selected number of channels can be electrically coupled to anelectrometer. In other embodiments, the MCP can be configured as a Zstack MCP, with three microchannel plates aligned in a shape thatresembles a Z. The Z stack MCP may have increased gain compared to asingle MCP.

In some instances, a plurality of microchannel plates may be stacked andconfigured such that each plate functions similar to a dynode. Oneillustration is shown in FIG. 17B where plates 1760, 1762, 1764, 1766and 1768 are stacked together. While not shown, one, two, three, four orall five of the plates may be electrically coupled to a respectiveelectrometer. The voltages applied to each plate may be controlled usingcircuits and configurations similar to those described in referenceherein to the dynodes. In some instances, stacked MCPs can be used as,or in, X-ray detectors, and by controlling the voltage applied toindividual plates, the gain of the detector can be automaticallyadjusted for each image to provide more clear images.

In certain examples, the MS device 1600 may be hyphenated with one ormore other analytical techniques. For example, MS devices may behyphenated with devices for performing liquid chromatography, gaschromatography, capillary electrophoresis, and other suitable separationtechniques. When coupling an MS device to a gas chromatograph, it may bedesirable to include a suitable interface, e.g., traps, jet separators,etc., to introduce sample into the MS device from the gas chromatograph.When coupling an MS device to a liquid chromatograph, it may also bedesirable to include a suitable interface to account for the differencesin volume used in liquid chromatography and mass spectroscopy. Forexample, split interfaces may be used so that only a small amount ofsample exiting the liquid chromatograph may be introduced into the MSdevice. Sample exiting from the liquid chromatograph may also bedeposited in suitable wires, cups or chambers for transport to theionization device 1620 of the MS device 1600. In certain examples, theliquid chromatograph may include a thermospray configured to vaporizeand aerosolize sample as it passes through a heated capillary tube.Other suitable devices for introducing liquid samples from a liquidchromatograph into a MS device will be readily selected by the person ofordinary skill in the art, given the benefit of this disclosure. Incertain examples, MS devices can be hyphenated to each other for tandemmass spectroscopy analyses. For example, one MS device may include afirst type of mass analyzer and the second MS device may include adifferent or similar mass analyzer as the first MS device. In otherexamples, the first MS device may be operative to isolate the molecularions, and the second MS device may be operative to fragment/detect theisolated molecular ions. It will be within the ability of the person ofordinary skill in the art, given the benefit of this disclosure, todesign hyphenated MS/MS devices at least one of which includes a boostdevice. Where two or more MS devices are hyphenated to each other, morethan a single detector can be used. For example, two or more detectorsmay be present to permit different types of detection of the ions.

In other embodiments, the detectors described herein may be used in aradioactivity detector to detect radioactive decay that provides ions orparticles. In particular, radionuclides that decay by alpha particleemission or Beta particle emission may be directly detected using thedetectors described herein. In general, alpha particle decay provides apositively charged particle of a helium nucleus. Heavy atoms such asU-238 decay by alpha emission. In beta particle emission, an electronfrom the nucleus is ejected. For example 1-131 (radioactive iodine) iscommonly used to detect thyroid cancer. The 1-131 ejects a beta particlewhich can be detected using one of the detectors described herein.

In certain embodiments, the detectors described herein may be present ina camera configured to detect beta particle emission and reconstruct animage of an object. For example, the detectors described herein can beused in a camera to provide an image, e.g., a digital image, and x-rayimages that can be displayed or stored in memory of the camera. In someembodiments, the camera may be configured to detect electron emissionfrom radioisotopes. The camera generally comprises one or more detectorsor arrays of detectors in a scan head. In some examples, one or more ofthe detectors of the array may comprise any one of the detectorsdescribed herein, e.g., a detector comprising dynodes electricallycoupled to respective electrometers. The scan head is typicallypositioned or can be moved over or around the object to electronsemission through a gantry, arm or other positioning means, e.g., an armcoupled to one or more motors. A processor, e.g., one present in acomputer system, functions to control the position and movement of thescan head and can receive input currents, calculate a mean input currentand use such calculated values to construct and/or store imagesrepresentative of the received electron emissions. The positioning ofthe detectors can provide spatial resolution as each detector ispositioned at a different angle relative to incident emission. As such,saturation of any one detector may occur with other detectors remainingunsaturated or becoming saturated at a different dynode. If desired, theprocessor can determine whether or not a dynode is saturated at any onedetector and then subsequently short other non-saturated dynodes ofother detectors at the same dynode. For example, if detector 1 of a sixdetector array is saturated at dynode 12, then signal amplification atother detectors can be terminated at dynode 12 to provide relative inputcurrents at the same dynode stage of different detectors, which can beused to provide spatial resolution and/or enhanced contrast for theimages. By terminating the signal amplification at the same dynodes ofdifferent detectors, the use of weighting factors can be omitted andimages can be constructed in a simpler manner. Alternatively, weightingfactors can be applied based on where saturation occurs at each detectorto reconstruct an image. For illustration purposes, one example of acamera is shown in FIG. 18. The camera 1800 is shown as including twodetectors 1820 and 1830 in a scan head 1810. Each of the detectors 1820,1830 may be configured as described herein, e.g., may include dynodeselectrically coupled to respective electrometers. If desired, thedetectors 1830, 1840 may be configured to be the same or may bedifferent. The detectors 1820, 1830 are each electrically coupled to aprocessor (not shown) that can receive signals from the detectors foruse in constructing an image. The camera 1800 can be used to create 2Dimages by placing the scan head on or near an object to be imaged andmeasuring electron emission at the site. Each of the detectors 1820,1830 is likely to receive different levels of electron emissions, whichcan be used to contrast an image of the object. For example, the variouselectron emission intensities can be coded, e.g., coded in greyscale orcolor-coded, to provide an image representative of the area under thescan head 1810.

In certain embodiments, the detectors described herein can be used inAuger spectroscopic (AES) applications. Without wishing to be bound byany particular scientific theory, in Auger spectroscopy electrons may beemitted from one or more surfaces after a series of internal events ofthe material. The electrons which are emitted from the surface can beused to provide a map or image of the surface at different areas.Referring to FIG. 19, a system for AES is shown. The system 1900comprises an electron source, e.g., an electron gun, 1910, provideselectrons to surface 1905. Electrons are emitted from the surface 1905and deflected into a cylindrical mirror analyzer (CMA) and onto thedetector 1920 for amplification. In the detector 1920, Auger electronsare multiplied as described herein in reference to FIGS. 1-12, forexample, and the resulting signal is sent to processor 1930. The devicecan be provided with power from power supply 1940. Collected Augerelectrons can be analyzed as a function of incident electron beam energyagainst the broad secondary electron background spectrum. The detector1920 may be any of the detectors described herein and can terminateamplification at a saturated dynode in real time without having tochange the gain of the detector for different incident energies providedby the electron gun 1910. If desired, AC modulation may be used alongwith signal derivatization to better analyze the surfaces. Otherdevices, e.g., scanning Auger microscopes, that measure signals fromAuger electrons may also be used. An image can be constructed of asurface and different surface heights can be displayed in differentshades of grey to provide a surface map.

In other examples, the detectors described herein may be used to performESCA (electron spectroscopy for chemical analysis) or X-rayphotoelectron spectroscopy. In general ESCA may be performed byirradiating a material with a beam of X-rays while measuring the kineticenergy of the number of electrons that escape for the upper surfaces,e.g., the top 1-10 nm, of the material. Similar to AES, ESCA is oftenperformed under ultra-high vacuum conditions. ESCA can be used toanalyze many different types of materials including, but not limited to,inorganic compounds, metal alloys, semiconductors, polymers, elements,catalysts, glasses, ceramics, paints, papers, inks, woods, plant parts,make-up, teeth, bones, medical implants, bio-materials, viscous oils,glues, ion modified materials and many others. Referring to FIG. 20, ablock diagram of a typical ESCA system is shown. The system 2000comprises an X-ray generator 2010, a sample chamber or holder 2020 onwhich a solid sample is typically added, and a detector 2030 all in ahousing 2005. One or more high vacuum pumps are typically present toprovide the ultra-high vacuum within the housing 1905. The sample holder2020 can be coupled to stage or moving platform to permit movement ofthe sample and analysis of different areas of the sample. The X-raygenerator 2010 provides X-rays 2015 that are incident on the surface2020. Electrons 2025 are ejected and received by the detector 2030. Thedetector 2030 may include collection lenses, an energy analyzer andother components as desired. The detector may also include one or moreof the detectors described herein, e.g., a detector comprising aplurality of dynodes with one or more dynodes electrically coupled to anelectrometer, to count the number of electrons arriving at the detector.Non-saturated dynodes can be averaged to determine a mean ion count at aparticular site of the sample. In addition, the ability of the detectorsdescribed herein to terminate amplification permits operation of thedetector at high gain values, which can lead to more sample precisemeasurements.

In certain configurations, the circuits and components described hereincan be used with a continuous electron multiplier. For example andreferring to FIG. 21, a continuous electron multiplier 2100 is shownthat comprises surfaces 2130-2137. Surface 2130 is the first surfacethat can receive ions and provide ejected electrons to surface 2134.Surface 2134 provides ejected electrons to surface 2132. Thisamplification can continue using the other surfaces. Each surface can beelectrically coupled to a respective electrometer similar to thedynode/electrometer pairs described herein. Signals from each surfacemay also be electrically isolated from signals from other surfaces.Where saturation is detected at a surface, the surface can be shortedout to protect downstream surfaces of the detector 2100. Signals fromthe various surfaces can be used to calculate currents, e.g., inputcurrent or output currents.

In certain embodiments, the detectors described herein can be used invacuum-ultraviolet (VUV) spectroscopic applications. VUV may be useful,for example, in determining the work functions of various materials usedin the semiconductor industry. VUV systems may include componentssimilar to those described in reference to ESCA and Auger spectroscopy.A VUV system may include a light or energy source that can scan itswavelength to provide a relationship between incident energy of thelight or energy source and the number of ejected electrons. Thisrelationship can be used to determine the gain of the material.

In some embodiments, the detectors described herein can be used inmicroscopy applications. For example, the arrangement of atoms on asurface of a material can be imaged using field ion microscopy. Themicroscope may include a narrow sampling tip coupled to a detector,e.g., a detector comprising a plurality of dynodes where one or moredynodes is electrically coupled to an electrometer or a multi-channelplate where one or more channels is coupled to a respectiveelectrometer. An imaging gas, e.g., helium or neon, can be provided to avacuum chamber and used image the surface. As the probe tip passes overthe surface, a voltage is applied to the top, which ionizes the gas onthe surface of the top. The gas molecules become positively charged andare repelled from the tip toward the surface. The surface near the tipmagnifies the surface as ions are repelled in a direction roughlyperpendicular to the surface. A detector can collect these ions, and thecalculated ion signal may be used to construct an atomic image of thesurface as the tip is scanned from site to site over the surface.

In some examples, the detector described herein can be used in anelectron microscope, e.g., a transmission electron microscope, ascanning electron microscope, a reflection electron microscope, ascanning transmission electron microscope, a low-voltage electronmicroscope or other electron microscopes. In general, an electronmicroscope provides an electron beam to an image, which scatters theelectrons out of the beam. The emergent electron beam can be detectedand used to reconstruct an image of the specimen. In particular, theemergent electron beam can be detected using one or more of thedetectors described herein, optionally with the use of a scintillant orphosphor screen if desired, to provide for more accurate measurements ofthe scattered electron beam. The beam can be scanned over the surface ofthe object and the resulting current measurements at each scan site canbe used to provide an image of the object. If desired, a detector arraycan be present so that spatial resolution may be achieved at each scansite to enhance the image even further.

In some instances, the detectors described herein can be used inatmospheric particle detection. For example, particles incident on theupper atmosphere from solar activity can be measured using the detectorsdescribed herein. The particles may be collected and/or focused into thedetector for counting. The resultant counts can be used to measure solaractivity or measure other astronomical phenomena as desired. Forexample, the detectors may be part of a particle telescope that measureshigh-energy particle fluxes or high-energy ion fluxes emitted from thesun or other planetary bodies. The measurements can be used to constructan image of the object, may be used in repositioning satellites or othertelecommunications equipment during high levels of solar activity or maybe used in other manners.

In certain examples, the detectors described herein can be used inradiation scanners such as those used to image humans or used to imageinanimate objects, e.g., to image baggage at screening centers. Inparticular, one or more detectors can be optically coupled to anon-destructive ion beam. Different components of the item maydifferentially absorb the ion beam. The resulting measurements can beused to construct an image of the baggage or other item that ismeasured.

In certain embodiments, the detectors described herein can be used todetect ions. For example, the detector can simultaneously detect aninput current signal at each dynode of a plurality of dynodes of anelectron multiplier configured to receive ions, and average the detectedinput current signals at each dynode comprising a measured current inputsignal above a noise current input signal and below a saturation currentinput signal to determine a mean electron multiplier input current. Ifsaturation is detected, the detector can terminate signal amplificationat a dynode where the saturation current is detected or at a dynodeupstream where the saturation current is measured to enhance protectionof the detector. In some embodiments, the detector can alter the voltageat a downstream dynode adjacent to the dynode where the saturationcurrent is measured to terminate the signal amplification. The exactmethodology used to calculate a mean input current can vary, and in someexamples, measured inputs from two, three, four or more dynodes are usedand averaged. For example, a mean input current can be calculated bycalculating the input currents at all dynodes and discarding calculatedinput currents below the noise current input signal and above thesaturation current input signal, and scaling each non-discardedcalculated input current by its respective electron multiplier gain andaveraging the scaled input currents to provide the mean electronmultiplier input current. In certain embodiments, the ions which aremeasured can be measured without adjusting the gain of the electronmultiplier. For example, a plurality of ions comprising differentmass-to-charge ratios can be measured without adjusting the gain of theelectron multiplier. In some instances, the number of ions per secondmay be determined using the detectors described herein. As noted herein,such operations are typically implemented using one or more processorswhich can receive and send suitable input and outputs to control thedetector.

In other embodiments, the detectors described herein may be configuredto simultaneously detect an input current signal of at least twointernal dynodes of a plurality of dynodes of an electron multiplierconfigured to receive ions, and average the detected input currentsignals at each of the at least two internal dynodes comprising ameasured current input signal above a noise current input signal andbelow a saturation current input signal to determine a mean electronmultiplier input current. If a saturated dynode is detected, then signalamplification at a dynode where a saturation current is measured can beterminated or termination may occur at a dynode downstream or upstreamfrom the dynode where saturation is detected. As discussed herein, it isnot necessary to measure the input current at each dynode but insteadthere may be simultaneous detection of an input current signal at everyother internal dynode of the plurality of dynodes, at every thirdinternal dynode of the plurality of dynodes, or other selected spacing.

In some embodiments, the detectors described herein may be configured toseparately control a bias voltage in each dynode of an electronmultiplier comprising a plurality of dynodes. As noted herein, byseparately controlling the bias voltage in the dynodes, changes incurrent during amplification do not substantially affect the biasvoltage. For example, the bias voltage can be controlled by regulatingthe dynode voltage to be substantially constant with increasing electroncurrent. Where such bias voltage are separately controlled, a mean inputcurrent can be calculated by calculating input currents at selecteddynodes of the plurality of dynodes, discarding calculated inputcurrents below a noise current input level and above the saturationcurrent input level, scaling each non-discarded calculated input currentby its respective gain, and averaging the scaled input currents todetermine a mean input current.

In other embodiments, the detectors described herein can be configuredto independently measure an input current at each of a plurality ofdynodes of an electron multiplier. In some examples, the methodcomprises calculating input currents at each dynode of the plurality ofdynodes, discarding calculated input currents below a noise currentinput level and above the saturation current input level, scaling eachnon-discarded calculated input current by its respective gain, andaveraging the scaled input currents to determine a mean input current.

In some examples, the detectors described herein can be used to analyzea sample by amplifying an ion signal from the sample by independentlymeasuring an input current at two or more of a plurality of dynodes inan electron multiplier comprising the plurality of dynodes. In certainembodiments, the method comprises calculating input currents at each ofthe two or more dynodes of the plurality of dynodes, discardingcalculated input currents below a noise current input level and abovethe saturation current input level, scaling each non-discardedcalculated input current by its respective gain, and averaging thescaled input currents to determine a mean input current. In someembodiments, the detector can be configured to measure input currentsfrom every other dynode of the plurality of dynodes or from otherselected spacing of dynodes.

In certain examples, the detectors described herein may be part of asystem which includes a plurality of dynodes, at least one electrometerelectrically coupled to one of the plurality of dynodes, and a processorelectrically coupled to the at least one electrometer, the processorconfigured to determine a mean input current from input currentmeasurements measured by the electrometer. If desired, the system caninclude a second electrometer electrically coupled to a dynode otherthan the dynode electrically coupled to the electrometer. In otherconfigurations, each of the plurality of dynodes is electrically coupledto a respective electrometer. In some instances, the processor may beconfigured to determine the mean input current by calculating inputcurrents at the at least one dynode of the plurality of dynodes,discarding calculated input currents below a noise current input leveland above the saturation current input level, scaling each non-discardedcalculated input current by its respective gain, and averaging thescaled input currents to determine a mean input current. In otherinstances, the processor may be configured to determine the mean inputcurrent by calculating input currents at the dynode electrically coupledto the electrometer and at the dynode electrically coupled to the secondelectrometer, discarding calculated input currents below a noise currentinput level and above the saturation current input level, scaling eachnon-discarded calculated input current by its respective gain, andaveraging the scaled input currents to determine a mean input current.In yet different configurations, the processor can be configured todetermine the mean input current by calculating input currents at eachdynode of the plurality of dynodes, discarding calculated input currentsbelow a noise current input level and above the saturation current inputlevel, scaling each non-discarded calculated input current by itsrespective gain, and averaging the scaled input currents to determine amean input current.

In certain embodiments, the detectors described herein, and theirmethods of using them can be implemented using a computer or otherdevice that includes a processor. The computer system typically includesat least one processor electrically coupled to one or more memory unitsto receive signals from the electrometers. The computer system may be,for example, a general-purpose computer such as those based on Unix,Intel PENTIUM-type processor, Motorola PowerPC, Sun U1traSPARC,Hewlett-Packard PA-RISC processors, or any other type of processor. Oneor more of any type computer system may be used according to variousembodiments of the technology. Further, the system may be located on asingle computer or may be distributed among a plurality of computersattached by a communications network. A general-purpose computer systemmay be configured, for example, to perform any of the describedfunctions including but not limited to: dynode voltage control,measurement of current inputs (or outputs), calculation of a mean inputcurrent, image generation or the like. It should be appreciated that thesystem may perform other functions, including network communication, andthe technology is not limited to having any particular function or setof functions.

Various aspects of the detectors and methods may be implemented asspecialized software executing in a general-purpose computer system. Thecomputer system may include a processor connected to one or more memorydevices, such as a disk drive, memory, or other device for storing data.Memory is typically used for storing programs and data during operationof the computer system. Components of the computer system may be coupledby an interconnection device, which may include one or more buses (e.g.,between components that are integrated within a same machine) and/or anetwork (e.g., between components that reside on separate discretemachines). The interconnection device provides for communications (e.g.,signals, data, instructions) to be exchanged between components of thesystem. The computer system typically is electrically coupled to a powersource and/or the dynodes (or channels) such that electrical signals maybe provided to and from the power source and/or dynodes (or channels) toprovide desired signal amplification. The computer system may alsoinclude one or more input devices, for example, a keyboard, mouse,trackball, microphone, touch screen, manual switch (e.g., overrideswitch) and one or more output devices, for example, a printing device,display screen, speaker. In addition, the computer system may containone or more interfaces that connect the computer system to acommunication network (in addition or as an alternative to theinterconnection device). The computer system may also include one moresingle processors, e.g., digital signal processors, which can be presenton a printed circuit board or may be present on a separate board ordevice that is electrically coupled to the printed circuit board througha suitable interface, e.g., a serial ATA interface, ISA interface, PCIinterface or the like.

In certain embodiments, the storage system of the computer typicallyincludes a computer readable and writeable nonvolatile recording mediumin which signals are stored that define a program to be executed by theprocessor or information stored on or in the medium to be processed bythe program. For example, dynode bias voltages for a particular routine,method or technique may be stored on the medium. The medium may, forexample, be a disk or flash memory. Typically, in operation, theprocessor causes data to be read from the nonvolatile recording mediuminto another memory that allows for faster access to the information bythe processor than does the medium. This memory is typically a volatile,random access memory such as a dynamic random access memory (DRAM) orstatic memory (SRAM). It may be located in the storage system or in thememory system. The processor generally manipulates the data within theintegrated circuit memory and then copies the data to the medium afterprocessing is completed. A variety of mechanisms are known for managingdata movement between the medium and the integrated circuit memoryelement and the technology is not limited thereto. The technology isalso not limited to a particular memory system or storage system.

In certain embodiments, the computer system may also includespecially-programmed, special-purpose hardware, for example, anapplication-specific integrated circuit (ASIC) or a field programmablegate array (FPGA). Aspects of the technology may be implemented insoftware, hardware or firmware, or any combination thereof. Further,such methods, acts, systems, system elements and components thereof maybe implemented as part of the computer system described above or as anindependent component. Although a computer system is described by way ofexample as one type of computer system upon which various aspects of thetechnology may be practiced, it should be appreciated that aspects arenot limited to being implemented on the described computer system.Various aspects may be practiced on one or more computers having adifferent architecture or components. The computer system may be ageneral-purpose computer system that is programmable using a high-levelcomputer programming language. The computer system may be alsoimplemented using specially programmed, special purpose hardware. In thecomputer system, the processor is typically a commercially availableprocessor such as the well-known Pentium class processor available fromthe Intel Corporation. Many other processors are available. Such aprocessor usually executes an operating system which may be, forexample, the Windows 95, Windows 98, Windows NT, Windows 2000 (WindowsME), Windows XP, Windows Vista, Windows 7 or Windows 8 operating systemsavailable from the Microsoft Corporation, MAC OS X, e.g., Snow Leopard,Lion, Mountain Lion or other versions available from Apple, the Solarisoperating system available from Sun Microsystems, or UNIX or Linuxoperating systems available from various sources. Many other operatingsystems may be used, and in certain embodiments a simple set of commandsor instructions may function as the operating system.

In certain examples, the processor and operating system may togetherdefine a computer platform for which application programs in high-levelprogramming languages may be written. It should be understood that thetechnology is not limited to a particular computer system platform,processor, operating system, or network. Also, it should be apparent tothose skilled in the art, given the benefit of this disclosure, that thepresent technology is not limited to a specific programming language orcomputer system. Further, it should be appreciated that otherappropriate programming languages and other appropriate computer systemscould also be used. In certain examples, the hardware or software isconfigured to implement cognitive architecture, neural networks or othersuitable implementations. If desired, one or more portions of thecomputer system may be distributed across one or more computer systemscoupled to a communications network. These computer systems also may begeneral-purpose computer systems. For example, various aspects may bedistributed among one or more computer systems configured to provide aservice (e.g., servers) to one or more client computers, or to performan overall task as part of a distributed system. For example, variousaspects may be performed on a client-server or multi-tier system thatincludes components distributed among one or more server systems thatperform various functions according to various embodiments. Thesecomponents may be executable, intermediate (e.g., IL) or interpreted(e.g., Java) code which communicate over a communication network (e.g.,the Internet) using a communication protocol (e.g., TCP/IP). It shouldalso be appreciated that the technology is not limited to executing onany particular system or group of systems. Also, it should beappreciated that the technology is not limited to any particulardistributed architecture, network, or communication protocol.

In some instances, various embodiments may be programmed using anobject-oriented programming language, such as SmallTalk, Basic, Java,C++, Ada, or C# (C-Sharp). Other object-oriented programming languagesmay also be used. Alternatively, functional, scripting, and/or logicalprogramming languages may be used. Various configurations may beimplemented in a non-programmed environment (e.g., documents created inHTML, XML or other format that, when viewed in a window of a browserprogram, render aspects of a graphical-user interface (GUI) or performother functions). Certain configurations may be implemented asprogrammed or non-programmed elements, or any combination thereof.

When introducing elements of the aspects, embodiments and examplesdisclosed herein, the articles “a,” “an,” “the” and “said” are intendedto mean that there are one or more of the elements. The terms“comprising,” “including” and “having” are intended to be open-ended andmean that there may be additional elements other than the listedelements. It will be recognized by the person of ordinary skill in theart, given the benefit of this disclosure, that various components ofthe examples can be interchanged or substituted with various componentsin other examples.

Although certain aspects, examples and embodiments have been describedabove, it will be recognized by the person of ordinary skill in the art,given the benefit of this disclosure, that additions, substitutions,modifications, and alterations of the disclosed illustrative aspects,examples and embodiments are possible.

1-80. (canceled)
 81. A method of detecting ions, the method comprising:simultaneously detecting an input current signal at each dynode of aplurality of dynodes of an electron multiplier configured to receiveions; and averaging the detected input current signals at each dynodecomprising a measured current input signal above a noise current inputsignal and below a saturation current input signal to determine a meanelectron multiplier input current.
 82. The method of claim 81, furthercomprising terminating signal amplification at a dynode where asaturation current is detected or at a dynode upstream where thesaturation current is measured.
 83. The method of claim 82, furthercomprising altering the voltage at a downstream dynode adjacent to thedynode where the saturation current is measured to terminate the signalamplification.
 84. The method of claim 81, further comprisingcalculating the mean input current by: calculating the input currents atall dynodes and discarding calculated input currents below the noisecurrent input signal and above the saturation current input signal, andscaling each non-discarded calculated input current by its respectiveelectron multiplier gain and averaging the scaled input currents toprovide the mean electron multiplier input current.
 85. The method ofclaim 81, further comprising providing a floating voltage to each dynodeof the plurality of dynodes.
 86. The method of claim 81, furthercomprising controlling the voltage at each dynode independently ofvoltage at the other dynodes of the plurality of dynodes.
 87. The methodof claim 81, further comprising measuring the ions without adjusting thegain of the electron multiplier.
 88. The method of claim 81, furthercomprising measuring a plurality of ions comprising differentmass-to-charge ratios without adjusting the gain of the electronmultiplier.
 89. The method of claim 81, further comprising calculatingthe amount of ions of a selected mass-to-charge ratio using thecalculated mean input current.
 90. The method of claim 81, furthercomprising calculating the amount of ions per second of a selectedmass-to-charge ratio using the calculated mean input current.
 91. Amethod of detecting ions, the method comprising: simultaneouslydetecting an input current signal of at least two internal dynodes of aplurality of dynodes of an electron multiplier configured to receiveions; and averaging the detected input current signals at each of the atleast two internal dynodes comprising a measured current input signalabove a noise current input signal and below a saturation current inputsignal to determine a mean electron multiplier input current.
 92. Themethod of claim 91, further comprising terminating signal amplificationat a dynode where a saturation current is measured.
 93. The method ofclaim 91, further comprising simultaneously detecting an input currentsignal at every other internal dynode of the plurality of dynodes. 94.The method of claim 91, further comprising simultaneously detecting aninput current signal at every third internal dynode of the plurality ofdynodes.
 95. The method of claim 91, further comprising terminatingsignal amplification at a dynode where a saturation current is measured.96. The method of claim 91, further comprising providing a floatingvoltage at each detected dynode of the plurality of dynodes.
 97. Themethod of claim 91, further comprising controlling the voltage at eachdynode independently of voltage at the other dynodes of the plurality ofdynodes.
 98. The method of claim 91, further comprising measuring theions without adjusting the gain of the electron multiplier.
 99. Themethod of claim 90, further comprising calculating the mean inputcurrent by: calculating the input currents at selected dynodes anddiscarding calculated input currents below the noise current inputsignal and above the saturation current input signal, and scaling eachnon-discarded calculated input current by its respective electronmultiplier gain and averaging the scaled input currents to provide themean electron multiplier input current.
 100. The method of claim 90,further comprising configuring the dynamic range of ion currentmeasurement is greater than 10¹⁰ for a 100 KHz reading. 101-133.(canceled)